Plant 10A/10B Intake Separation, Condensate Stripping and Gas Compression
Plant 10 consists of three major sections:
Gas leaving the offshore platforms is cooled and partially condensed in the undersea pipeline by the cold ocean water (50-65° F).
The gas is pipelined from the offshore platform at a design sour gas feed rate of 60 MMscfd. The feed crosses the plant boundary at about 800 psig, passes through the flow control manifold, and enters the intake separator, V-1000 which separates any entrained liquid from the sour gas. The liquid-free sour gas goes to the Acid Gas Removal Plants for H2S and C02 removal. Any entrained liquid collected in V-1000 flows by gravity to the condensate surge vessels, V-1001A and B.
Hydrocarbon condensate is removed daily when the pipeline is pigged. As the line is pigged, a liquid slug of up to 2000 bbl enters V-1000 over a 10-30 minute period. These liquids are then sent to V-1001A and B by gravity flow. The main process objective of V-1001A and B is to hold the pipeline liquids and feed the downstream units at a steady rate.
Additional liquids are recovered as the flashed gas from the Oil Plant Stabilization Unit is compressed in the intake gas compression section. The recovered condensate is fed continuously to V-1001A and B at a design rate of about 3100 BPOD.
The hydrocarbon condensate leaving V-1001A and B is filtered in condensate filters, F-1000A and B, before being routed to the condensate stripper, C-1020. F-1000A and B remove solids that could cause plugging, erosion, and corrosion in the downstream processing equipment.
Condensate stripping is required to remove methane, ethane, and H2S which are dissolved in the condensate, due to the high pressure in the condensate surge vessels. These components would otherwise end up in the propane product causing the vapor pressure to exceed specification. Also, excessive amounts of H2S in the condensate may overload the liquid treating plant resulting in a sour propane product.
Hydrocarbon condensate from V-1001A and B is flashed from 650 psig to 225 psig and enters the top tray of C-1020. The design feed rate is 6300 BPOD and the normal feed rate is 5534 BPOD. C-1020 contains 20 valve trays which provide the gas/liquid contacting for effective stripping. As the liquid flows down and across the trays in the column, hot vapors rising up through the valves on the trays strip out light hydrocarbons and H2S. Hot vapors from the column overhead enter second-stage knockout drum, V-1010B, in the intake gas compression system.
The column bottom is divided into two compartments so that all liquid from the bottom tray passes through stripper reboiler, E-1020. This minimizes light components in the product condensate. The reboiler inlet compartment runs full to provide a constant static head for reboiler circulation.
E-1020 partially vaporizes the liquid to remove light ends and to produce stripping vapors. These vapors enter the column below the bottom tray. Net liquids from E-1020 flow back into the reboiler compartment. Liquid from the reboiler compartment overflows into the net bottoms compartment. Product condensate from this compartment is sent to the debutanizer, C-1600, in Plant 16.
Heat is supplied to E-1020 by condensing 80 psig steam on the tube-side of the reboiler. Steam condensate is collected in reboiler condensate pot, V-1020, located directly beneath E-1020, and then routed to condensate collection drum, V-1620, in Plant 16.
The intake gas compression system compresses flashed gas from the Oil Plant Stabilization Unit and the Condensate Stripper and sends it to the Acid Gas Removal Plants. The gas compression system consists of two 100% reciprocating compressors, K-1010A and B. Each compressor is a two-stage machine. The first stage is designed to compress 3.6 MMscfd of gas from 35 psig to 180 psig. The second stage is designed to compress 6.2 MMscfd of gas from 175 psig to 675 psig.
Flashed gas from the Oil Plant and the rich amine flash drums in Plants 11 and 21 are combined and fed to the compressor precooler, E-1009 which cools the combined gas stream from about 203° F to 122° F.
The cooled gas from E-1009 combines with additional gas streams from the glycol flash drum, pipeline pig catcher, and first-stage compressor spillback. This stream flows to the first-stage compressor knockout drum, V-1010A, which removes condensed liquid.
Gas from V-1010A enters the first stage of the intake gas compressor, K-1010A and B. Gas leaving the first stage is cooled from 220° F to 120° F in the interstage cooler, E-1010A. The partially condensed vapor from E-1010A is combined with the overhead gas from the condensate stripper, C-1020, and the second-stage compressor spillback. The combined stream flows to the second-stage knockout drum, V-1010B, where condensed liquid is removed.
The second-stage compression is similar to the first-stage compression. The gas leaving the second-stage compressor is cooled in aftercooler, E-1010B. The partially condensed vapors from E-1010B are routed to the second-stage aftercooler knockout drum, V-1010C. The liquid-free vapors from V-1010C are combined with the overhead gas from V-1000 and sent to the Acid Gas Removal Plants.
Compressor knockout drums, V-1010A, B and C, are three-phase separators. Condensed free water from the bottom of each vessel is routed to the water degasser, V-1015. The condensed hydrocarbon liquid is pumped to the condensate surge vessels, V-1001A and B. A portion of the hydrocarbon liquid from V-1010A may be routed to the electrostatic coalescers in the Oil Plant.
The free water from the condensate surge vessels, V-1001A and B, and the compressor knockout drums, V-1010A, B, and C, enters water degasser, V-1015. V-1015 removes dissolved H2S and light hydrocarbons from the water. The water streams are flashed at 5 psig in V-1015. This causes most of the dissolved gases to come out of solution. There are three splash trays in V-1015 to agitate the water and improve the degassing process. The overhead gases are sent to vapor recovery. The degassed sour water is pumped to the oily water surge tank in the Oil Plant.